1) Field of the Invention
The invention relates to a process for the preparation of bitumen/polymer compositions with a very low temperature susceptibility. It further relates to the application of the compositions obtained to the production of bitumen/polymer binders for the preparation of coatings and in particular of road surfacings, of bituminous mixes or alternatively of watertight facings.
2) Background Art
It is known to use bituminous compositions as various surface coatings and in particular as road surface coatings, provided that these compositions possess a certain number of essential mechanical qualities.
These mechanical qualities are assessed, in practice, by determining, by standardized tests, a series of mechanical characteristics, the most widely used of which are as follows:
softening point, expressed in .degree. C. and determined by the ring-and-ball test defined by NF Standard T 66008, PA1 brittleness point or Fraass point, expressed in .degree. C. and determined according to IP Standard 80/53, PA1 penetrability, expressed in 1/10of an mm and determined according to NF Standard T 66004, PA1 tensile rheological characteristics determined according to NF Standard T 46002 and comprising the quantities: PA1 (a) random copolymers of ethylene and of a monomer B chosen from acrylic acid, methacrylic acid, maleic acid or its anhydride, glycidyl acrylate and glycidyl methacrylate which contain, by weight, 80% to 99.7% and preferably 85% to 99.5% of ethylene; PA1 (b) random terpolymers of ethylene, of a monomer A chosen from vinyl acetate and alkyl acrylates or methacrylates containing a C.sub.1 to C.sub.6 alkyl residue, such as methyl, ethyl, propyl, butyl or hexyl, and of a monomer B chosen from acrylic acid, methacrylic acid, maleic acid or its anhydride, glycidyl acrylate and glycidyl methacrylate which contain, by weight, 0.5% to 40% of units resulting from the monomer A and 0.5% to 15% of units resulting from the monomer B, the remainder being formed of units resulting from ethylene; and PA1 (c) copolymers resulting from the grafting of a monomer B, chosen from acrylic acid, methacrylic acid, maleic acid or its anhydride, glycidyl acrylate and glycidyl methacrylate, on a substrate composed of a polymer chosen from polyethylenes, in particular low density polyethylenes, polypropylenes and random copolymers of ethylene and of vinyl acetate or of ethylene and of alkyl acrylate or methacrylate containing a C.sub.1 to C.sub.6 alkyl residue, such as methyl, ethyl, propyl, butyl or hexyl, which contain, by weight, 40% to 99.7% and preferably 50% to 99% of ethylene, the said grafted copolymers containing, by weight, 0.5% to 15% of grafted units resulting from the monomer B. PA1 (i) random terpolymers of ethylene, of alkyl acrylate or methacrylate containing a C.sub.1 to C.sub.6 alkyl residue, such as methyl, ethyl or butyl, and of maleic anhydride which contain, by weight, 0.5% to 40% of units resulting from alkyl acrylate or methacrylate and 0.5% to 15% of units resulting from maleic anhydride, the remainder being formed of units resulting from ethylene; PA1 (ii) random terpolymers of ethylene, of alkyl acrylate or methacrylate containing a C.sub.1 to C.sub.6 alkyl residue, such as methyl, ethyl or butyl, and of glycidyl acrylate or methacrylate which contain, by weight, 0.5% to 40% of units resulting from alkyl acrylate or methacrylate and 0.5% to 15% of units resulting from glycidyl acrylate or methacrylate, the remainder being formed of units resulting from ethylene; PA1 (iii) low density polyethylenes grafted with maleic anhydride and polypropylenes grafted with maleic anhydride which contain, by weight, 0.5% to 15% of grafted units resulting from maleic anhydride; PA1 (iv) low density polyethylenes grafted with glycidyl acrylate or methacrylate and polypropylenes grafted with glycidyl acrylate or methacrylate which contain, by weight, 0.5% to 15% of grafted units resulting from the glycidyl derivative, are particularly preferred.
yield stress .sigma..sub.y in bars, PA2 elongation at yield stress .epsilon..sub.y in %, PA2 breaking stress .sigma..sub.b in bars, PA2 elongation at break .epsilon..sub.y in %.
It is also possible to obtain an indication of the temperature susceptibility of bituminous compositions from a correlation between the penetrability (abbreviated to pen) and the softening point (abbreviated to RBT) of the said compositions known under the name of Pfeiffer number (abbreviated to PN).
This number is calculated from the relationship: ##EQU1## in which A is the slope of the straight line represented by the equation: ##EQU2##
The temperature susceptibility of the bituminous composition decreases as the value of the Pfeiffer number increases or, which comes to the same thing, as the value of the quantity A decreases. For conventional bitumens, the Pfeiffer number takes values lying in the vicinity of zero.
In general, conventional bitumens do not simultaneously exhibit all the required qualities and it has been known for a long time that the addition of varied polymers to these conventional bitumens makes it possible to favourably modify the mechanical properties of the latter and to form bitumen/polymer compositions having improved mechanical qualities with respect to those of the bitumens alone.
The incorporation of olefinic polymers functionalized by epoxy or carboxyl groups in bituminous compositions composed of one or more bitumens or composed of one or more bitumens and of one or more polymers not containing such groups results in the production of bitumen/polymer compositions with significantly improved consistency (increase in the ring-and-ball softening point), temperature susceptibility (increase in the Pfeiffer number) and tensile mechanical properties.
Such bitumen/polymer compositions, which contain olefinic polymers functionalized by epoxy or carboxyl groups, are described in particular in the references U.S. Pat. Nos. 4,650,820, 5,306,750 and 5,331,028, as well as in the French patent application filed by the Applicant Company on Oct. 11, 1994 under the number 9413537. Thus, the reference U.S. Pat. No. 4,650,820 relates to a bitumen/polymer composition containing, by weight, 95% to 99% of a bitumen having a pseudoviscosity at 30.degree. C. lying in the range 200 to 1000 seconds and 1% to 5% of a terpolymer composed of 88% to 98.7%, on a molar basis, of units deriving from ethylene, of 1% to 10%, on a molar basis, of units deriving from at least one C.sub.1 to C.sub.6 alkyl acrylate or methacrylate and of 0.3% to 3% of units deriving from maleic anhydride.
The reference U.S. Pat. No. 5,306,750 describes a bitumen/polymer composition consisting of a reaction product obtained by bringing a bitumen into contact, at temperatures of 125.degree. C. to 250.degree. C. and with stirring for a period of time of the order of 3 hours to 48 hours, with an ethylene copolymer containing, by weight, 0.1% to 20% of glycidyl groups, the amount of the copolymer representing 0.05% to 20% of the weight of the composition. In particular, the ethylene copolymer containing glycidyl groups is a random copolymer of ethylene, of 0.5 to 15% by weight of a monomer containing a glycidyl group, in particular glycidyl acrylate or methacrylate, and of 0 to 50% by weight of a vinyl monomer without glycidyl group, such as a vinyl ester, such as vinyl acetate, or an alkyl acrylate or methacrylate. The reference U.S. Pat. No. 5,331,028 relates to a bitumen/polymer composition of a type comparable to that described in the reference U.S. Pat. No. 5,306,750 but additionally containing 0.3% to 20% by weight of a block copolymer of styrene and of a conjugated diene, for example block copolymer of styrene and of butadiene, having a weight-average molecular mass ranging from 100,000 to 1,000,000. The subject of French Patent Application No. 9413537 is a bitumen/polymer composition obtained by bringing a bitumen or mixture of bitumens, a sulphur-crosslinkable elastomer, such as, in particular, a block copolymer of styrene and of a conjugated diene, an olefinic polymer containing epoxy or carboxyl (COOH) functional groups and a sulphur-donor coupling agent into contact between 100.degree. C. and 230.degree. C., with stirring.